The present invention relates to a fabrication process of performing the chemical vapor deposition (CVD) on silicon wafers and, more particularly, to an application of controlling gas valves to reduce particles from the CVD process.
It is an important process for semiconductors using the CVD process to form an insulating layer or a thin film layer of silicon dioxide on the surface of a wafer placed in water vapor or oxygen. This process is performed in a reaction chamber connected with transport pipes. The transport pipe is designed to have a plurality of gas valves. The amount of gas flowing into the reaction chamber is controlled by opening or closing the gas valves. In the CVD process, because oxygen easily reacts with highly active gases, particles will form and thus precipitate in a valve. If the particles flow into the reaction chamber along with the gases, the insulating layer or the thin film layer will not grow uniformly on the wafer when performing the CVD process. Defects on the wafer will let the integrated circuits formed on the wafer be problematic. Therefore, the use value of the wafer will be reduced, resulting in waste of production.
The prior art method of resolving the problem of particles is described below. First, the gas valves are opened to let an inert gas flow through the transport pipe and the gas valves and then into the reaction chamber during the idle period of the reaction chamber. Next, the gas valves are closed and a pump is used to extract the gas and the particles out so as to purge the gas valves and the reaction chamber. Although the count of undesirable wafers can be effectively reduced by the actions of opening and closing the gas valves described above during the idle period of the reaction chamber, the possibility of a wafer generating particles in the CVD process to fall onto the next wafer cannot be reduced. Therefore, the yield of wafer will be deteriorated. The present invention aims to propose a method of clearing particles so that the above problems in the prior art can be resolved.
The primary object of the present invention is to provide an application of controlling gas valves to reduce particles from the CVD process so that the yield of wafer can be increased under the premise that the production is not influenced.
According to the present invention, the application of controlling gas valves to reduce particles from the CVD process is described below. First, the actions of opening and closing a gas valve are added to let the particles possibly adhering on the valve fall during the idle period between the CVD processes of a wafer and the next wafer. Next, an inert gas is led in to purge the gas valve and the reaction chamber. Finally, a pump is used to extract the gas out. Thereby, the possibility of particles entering the reaction chamber during the CVD process of the next wafer can be prevented.